Synthesis gas (or “syngas”) is a mixture of primarily hydrogen and carbon monoxide, commonly with carbon dioxide, methane, water, nitrogen, and possibly other constituents such as argon or helium. Syngas can be produced from any carbon containing feedstock, including natural gas, heavy petroleum cuts such as resid or coke, bitumen, coal, or biomass by a variety of processes. Natural gas may be converted to synthesis gas using steam methane reforming (“SMR”), carbon dioxide reforming (“dry reforming”), or a combination of these two processes, or by processes employing air, enriched air, or oxygen (generally with some steam addition) such as combined reforming, autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”) or thermal partial oxidation (“POX”). When employed, enriched air or oxygen may be produced by conventional cryogenic air separation, pressure swing adsorption (“PSA”) or membrane processes, the use of ion transport membranes (“ITM”) or any other method producing a gas containing sufficient oxygen. Heavier liquids or solids, such as petroleum cuts and/or coal, are typically converted to synthesis gas by processes employing air, enriched air, or oxygen such as gasification and catalytic/thermal partial oxidation, again typically with some steam addition to the reaction mixture. Numerous synthesis gas production processes are well known in the art.
Liquid hydrocarbon products and oxygenates may be produced from synthesis gas using any of a number of known processes. The liquid hydrocarbon products are referred to herein as “synthetic crude.” As used herein, the term oxygenate means any of (1) ethers, including, for example, ethyl tert-butyl ether (ETBE), diisopropyl ether (DIPE), dimethyl ether (DME), methyl tert-butyl ether (MTBE), tert-amyl ethyl ether (TAEE), tert-amyl methyl ether (TAME); and (2) methanol and C2+ alcohols, including for example, ethanol (EtOH), propanol, butanol, tert-amyl alcohol (TAA), and tert-butyl alcohol (TBA). Methanol is the most common oxygenated product synthesized from syngas.
Small and micro scale processes, including processes utilizing certain portable equipment, are described in detail in U.S. application Ser. No. 12/040,500 filed on Feb. 29, 2008, entitled “Fischer-Tropsch and Oxygenate Synthesis Catalyst Activation/Regeneration in a Micro Scale Process,” the disclosure of which is incorporated by reference herein in its entirety.
Conventional Plant Start-Up Configuration
For a fixed-location land-based synthesis gas conversion plant (i.e., >500 bbl/day), there are a limited number of possibilities for performing FT or oxygenate synthesis plant start-ups. At one end of the spectrum, the plant is permanently connected to a large(r) electrical grid system, whereby at least some external (to the plant) electrical power is available at essentially all times. In this configuration, operation of all necessary start-up facilities and/or utilities (including, for example, the plant monitoring and control system, distilled and/or reverse osmosis water systems, inert gas generation, and/or start-up boilers) can be powered from external sources of electric power, e.g., a local power grid.
At the other end of the spectrum, for example in a completely remote plant site, stand alone, natural gas and/or liquid fuel (e.g., diesel) start-up generators are typically provided to power all necessary start-up facilities and/or utilities. Because such facilities will generally require a number of on-site workers, there are a number of additional systems, such as lighting, heating/vacuum/air conditioning (HVAC), potable water, sanitary sewers, computers, and communications, that must also be maintained in operation. Consequently, some source of electrical power must be continuously provided in such remote plant sites.
There are, of course, a number of conceivable intermediate configurations between these extremes. For example, a small natural gas and/or liquid fuel generator could be provided with sufficient output to power a start-up steam boiler and the boiler's control system. Once the boiler system and an associated steam turbine electrical generator are in operation, the remainder of the plant systems can be started up, utilizing the power from the steam turbine electrical generator. A natural gas fired turbine and/or micro-turbine electrical generator may be employed in a nearly identical way.
Regardless of the initial source of start-up power, all known synthesis gas-based FT and/or oxygenate synthesis processes produce large quantities of excess heat, particularly in the syngas generation and FT/oxygenate synthesis steps. Even for steam methane reforming generation of synthesis gas—which is typically known as an endothermic reaction—there is a great deal of excess energy in the combustion fuel gas stream which is used to supply the SMR reaction heat. The exothermic energy of syngas generation and liquid hydrocarbon and/or oxygenate synthesis is typically captured and employed to provide electrical and/or mechanical power for an entire plant during normal operations through the use of steam and/or other heat transfer medium such as hot oil.
Steam may be directly employed as both a heating medium and source of rotating equipment shaft energy (i.e., steam turbine driven compressors), while electrical power generation may include both steam- and (external feed and/or tail) gas-turbine generators. In some instances, there may be significant excess exothermic energy available after providing all required plant power, so that in non-remote locations or in more remote locations where a local external electric grid exists overall plant/project economics may be greatly improved through electrical power sales.
Movable Plant Start-Up Configuration
For currently-proposed movable, predominantly offshore, plants practical options for the plant start-up power supply are generally limited to local power generation. Therefore, such synthesis plants are generally provided with start-up power generation facilities in the same manner as a completely isolated, land-based synthesis plant would be. An off-shore synthesis plant as part of a larger facility such as an oil production platform, barge, or ship, would typically be able to employ the larger facility's local electrical power grid.
Small or micro scale liquid hydrocarbon and/or oxygenate synthesis units, however, may not, in some instances, be able to support the economics of providing complete start-up power generation equipment dedicated solely to the small or micro scale unit.